In recent years, in view of savings in resources and conservation of energy, there have been increasing demands for nickel-hydrogen secondary batteries, nickel-cadmium secondary batteries, lithium ion secondary batteries, etc. which can be used repeatedly. Among them, lithium ion secondary batteries are characterized by lightness in weight, high electromotive force, and high energy density. Thus, there are growing demands for the lithium ion secondary batteries as power sources for driving various kinds of mobile electronic devices and portable communication devices such as mobile phones, digital cameras, video cameras, and laptop personal computers.
On the other hand, to reduce used amount of fossil fuel, and to reduce the amount of emission of CO2, expectations for battery modules are growing to serve as power sources for driving motors such as vehicles. Such a battery module includes two or more batteries to obtain a preferable voltage and preferable capacity.
In development of the battery module, along with the safety of batteries themselves, the safety of the battery module which is a collection of the batteries becomes more important. That is, a battery may lose its function as a battery due to over-charge, over-discharge, an internal short-circuit, or an external short-circuit. Moreover, the internal pressure of a battery may be increased by gas generated due to over-charge, over-discharge, an internal short-circuit, or an external short-circuit, which may possibly break an outer case of the battery. Thus, in the battery module in which a plurality of batteries is integrated, it is important to prevent the performance of the entirety of the battery module from being degraded due to a problem in one battery.
As a means to address the problems as described above, for example, a battery module in which a portion connecting batteries to each other is provided with a temperature sensor configured to break the connection when a current equal to or higher than a predetermined value flows is disclosed (for example, PATENT DOCUMENT 1). Moreover, a battery module including a fuse formed between batteries connected in series by a metal interconnect printed on an insulating substrate is disclosed (for example, PATENT DOCUMENT 2).